CN1768018A - Explosive composition comprising heavy ANFO and a plant derived, inert bulking and sensitizing additive - Google Patents

Abstract

An explosive composition is provided that is comprised of a HeavyANFO and grain hulls. In one embodiment, the grain hulls are com prised of rice hulls. The grain hulls serve both as an inert bulking additive that reduces the density of the composition and as asensitizer that reduces the energy needed to reliably detonate t he composition. Also provided is a method for manufacturing an explosive composition comprised of Heavy ANFO and grain hulls, suchas rice hulls. Additionally, a method of using an explosive comp rised of ANFO and grain hulls in a mining operation is disclosed.

Description

Explosive compositions comprising heavy ANFO and plant derivatives and inert bulking and sensitizing additives

technical field

The invention relates to an explosive composition, which includes ammonium nitrate fuel oil ANFO (Ammonium Nitrate Fuel Oil), a method for preparing the explosive composition, and a method for using the explosive composition.

Background technique

One of the most common explosives that has been used in mining operations for many years is ANFO, which consists of porous ammonium nitrate particles and diesel fuel within the interstices of the porous ammonium nitrate particles. In mining operations, the use of ANFO generally involves drilling blast holes in the soil to be mined. After the blast hole has been drilled, one or more detonators and ANFO are loaded into the blast hole. The ANFO is then detonated, with the result that the soil to be mined is broken up in a manner that is easily removed mechanically for further processing. The blastholes are usually arranged in an array and the ANFOs arranged in the blastholes are fired simultaneously or in a designed order to produce the desired blast characteristics.

The disadvantage associated with ANFO is that it is highly absorbent and absorbing water reduces the explosive ability of ANFO. Therefore, ANFO is generally not used in situations where water in a blast hole may adversely affect ANFO. The water may be the water present in the blasthole when the ANFO is loaded and/or the water that migrates into the blasthole after the ANFO is loaded and before the ANFO is detonated. Due to the high water absorption of ANFO, ANFO is suitable for applications where water is unlikely to significantly reduce the effect of ANFO. Additionally, when ammonium nitrate is mixed with fuel oil to form ANFO, the resulting composition is dry to the touch and is therefore often referred to as a "dry blend" explosive.

To address the "wet blast hole" situation, water-resistant ANFOs, commonly referred to as heavy ANFOs, were developed. Heavy ANFO contains emulsion explosives mixed with ANFO and/or ammonium nitrate particles. Emulsion explosives contain an oxidizing agent dissolved in water droplets surrounded by an immiscible fuel such as oil. Due to the water resistance of heavy ANFO, it is suitable for applications where the composition will be or may be exposed to water. Additionally, heavy ANFO is wet to the touch because the interstices inside the ammonium nitrate are filled with the emulsion explosive. For this reason, heavy ANFO is sometimes referred to as a "wet mix" explosive.

In addition to water resistance, a given volume of heavy ANFO has greater explosive energy than an equal volume of ANFO. In mining, the greater blast energy per unit volume of heavy ANFO generally means that fewer blast holes need to be drilled to blast a given area compared to the number of blast holes that need to be drilled when ANFO is used. Also, in many cases, for a given detonation energy, it is cheaper to make heavy ANFO than it is to make ANFO. Heavy ANFO is also used in dry blast hole situations due to increased blast energy and reduced cost.

The problem with heavy ANFO is that the density of heavy ANFO in a blasthole increases with the depth of the blasthole. In other words, there is a density gradient of heavy ANFO in the blasthole. As the density of heavy ANFO increases, the sensitivity of heavy ANFO decreases. Sensitivity is a measure of the energy required to detonate an explosive reliably. Therefore, less energy is required to detonate a more sensitive explosive than a less sensitive explosive. Therefore, in a blast hole, heavy ANFO near the bottom of the blast hole may be less sensitive than heavy ANFO near the top of the blast hole. This sensitivity gradient can produce an asymmetric or non-uniform detonation which does not have the desired explosive characteristics.

To address the density problem in heavy ANFO, many solutions have been proposed. For example, some inert bulking agents in the form of agricultural waste are added to heavy ANFO. However, the currently known agricultural wastes used to reduce density also desensitize explosives, in many cases even to the point of rendering them ineffective. Another approach is to replace some or all of the fuel oil in heavy ANFO with polystyrene. However, this method also reduces the sensitivity of the explosive and is often cost prohibitive. Yet another approach is to use microspheres and/or perlite, which are known sensitizers, to reduce the density of heavy ANFO. This approach is currently not considered cost effective. Another approach is to use chemical aeration to reduce density. The disadvantage of this method is that it cannot effectively control the density over a wide range of densities.

Contents of the invention

The present invention relates to an explosive composition comprising heavy ANFO and plant derivatives, and inert bulking and sensitizing additives. The explosive composition is wet to the touch and therefore is not considered a "dry mix" explosive. In one embodiment, the inert bulking and sensitizing additive comprises grain husks, wherein each grain husk has a plurality of voids. Additionally, the inert bulking and sensitizing additive is substantially free of any other components of the grain other than the hull. In one embodiment, the grain hulls are rice hulls.

In another embodiment, the inert bulking and sensitizing additive comprises grain hulls which are characterized by a large number of voids. Also, the grain hull is no longer naturally attached to any other components of the grain. In one embodiment, the grain hulls are rice hulls. In other embodiments, the composition is substantially free of other components of the grain other than the hull.

Yet another embodiment of the present invention relates to a process for the preparation of heavy ANFO with vegetable derivatives, ie inert bulking and sensitizing additives. In one embodiment, the method comprises the steps of: (a) providing a mixer; (b) loading the mixer with an emulsion explosive; (c) loading the mixer with an ammonium nitrate-based explosive after the emulsion explosive has been added to the mixer a mixer; (d) using a mixer to mix emulsion explosives and ammonium nitrate-based explosives to produce heavy ANFO; and (e) using a mixer to mix said heavy ANFO with inert bulking and sensitizing additives including grain hulls, said Grain husks are characterized by having many voids. In one embodiment, the grain hulls comprise rice hulls.

Other embodiments of the invention relate to a method of making an explosive composition comprising heavy ANFO and grain hulls. The method involves providing an end-to-end level blender and then utilizing the blender to blend heavy ANFO and grain hulls to produce an explosive composition with a high degree of homogeneity. In yet another embodiment, the mixer is also used to mix heavy ANFO constituents.

Yet another embodiment of the present invention is directed to a method of using an explosive composition comprising heavy ANFO and grain hulls. The method includes providing an explosive composition comprising heavy ANFO and grain hulls; and loading the explosive composition into a blasthole. In other embodiments, the method includes mixing heavy ANFO and grain hulls to make an explosive composition; and mixing at a property where a blast hole is located. Yet another embodiment involves the mixing of heavy ANFO and grain hulls on a moving platform.

Detailed ways

The present invention relates to an explosive composition comprising heavy ANFO and plant derivatives, ie inert bulking and sensitizing additives.

Heavy ANFO consists of emulsion explosives mixed with ANFO and/or ammonium nitrate. The emulsion explosive comprises: (a) a dispersed phase having an aqueous solution of one or more oxidizer salts; and (b) a continuous phase having an oil and an emulsifier. Suitable oxidizing salts include ammonium nitrate, sodium nitrate and calcium nitrate. Other oxidizing agents for explosives known to those skilled in the art or documented in the literature are also feasible, including but not limited to urea, iron oxide, lead dioxide, ammonium perchlorate, barium nitrate, barium peroxide, Lead, potassium chlorate, sodium chlorate, potassium perchlorate, sodium perchlorate, etc. Typically, the oxidizing agent or oxidizing agents are concentrated in an aqueous solution and can be saturated in the aqueous solution. The oil is generally fuel oil or diesel or a mixture thereof. However, other oils known to those skilled in the art or documented in the literature for explosives are also feasible, including but not limited to waste oil, bunker oil and mineral oil. Potential substitutes for oil are coal dust and rubber. Any of the many emulsifiers for explosives known to those skilled in the art or documented in the literature will work. Many suitable emulsifiers feature esters or other derivatives of monohydric or polyhydric alcohols in combination with long-chain components or other lyophilic materials.

A typical explosive emulsion used in heavy ANFO comprises about 40-80% by weight ammonium nitrate; about 0-40% by weight calcium nitrate; about 0-15% by weight sodium nitrate; about 10-25% by weight water; and About 5-12% by weight of fuel oil.

ANFO contains ammonium nitrate and fuel oil. Typically, the ammonium nitrate is in the form of porous ammonium nitrate particles. However, other forms of ammonium nitrate can also be used to prepare ANFO, including but not limited to agricultural grade ammonium nitrate granules, crystallized ammonium nitrate, and ground ammonium nitrate. However, these other forms of ammonium nitrate generally yield lower quality ANFO compared to ANFO made from porous ammonium nitrate particles. If desired, some of the ammonium nitrate may be replaced by one or more other oxidizing agents such as those mentioned in emulsion explosives. As used herein, fuel oil refers to any liquid petroleum product that is combusted in heat generating furnaces or used in engines that generate power. Additionally, the term fuel oil includes: (a) suitable substitutes for such liquid petroleum products, such as mineral oil; and (b) mixtures of such liquid petroleum products with suitable substitutes.

Vegetable derivatives, ie inert bulking and sensitizing additives include cereal hulls which are characterized by each having a large number of voids which are often called microvoids due to their small size. The microvoids serve to create so-called "hot spots" or void volumes which, all other factors being equal, increase the sensitivity of the explosive composition. Cereal hulls also reduce the density of the explosive composition, all other factors being equal. Thus, the effect of the grain hull is to both reduce density and increase sensitivity. In one embodiment, the additive includes grain hulls, but is substantially free of any other components of the grain other than the grain hulls. In another embodiment, the explosive composition comprises grain husks, but is substantially free of any other components of the grains other than the grain husks, in other words, no other components of the grains are used in the explosive composition other than the grain husks other purposes in the object. In yet another modified embodiment, the additive includes grain hulls and another component that acts to reduce explosive density and/or increase explosive sensitivity and is about the same size as the grain hulls.

One grain hull that has many microvoids and can act as an inert bulking agent to reduce the density of explosive compositions is rice hulls. For a discussion of the microvoid properties of rice hulls, see Chapter 19 in Rice: Chemistry and Technology by Bienvenido O. Juliano, which is incorporated herein by reference. The rice hulls also have a waxy layer that complements the water-repelling properties of heavy ANFO. However, any other type of grain hull that has microvoids and is capable of acting as an inert bulking agent is also feasible.

The ranges of raw materials for explosive compositions comprising heavy ANFO and plant derivatives (ie inert bulking and sensitizing additives) are listed in Table I below.

Table I raw material Min % maximum% weight ammonium nitrate 50 99 calcium nitrate 1 20 ^* sodium nitrate 1 20 ^* fuel phase 1 10 water 1.5 12 inert bulking agent 1 25 ^**

^* Maximum % of mixture of calcium nitrate and sodium nitrate is 20%

^** % relative to final blend of heavy ANFO and grain hulls

It should be noted that it is assumed that the compositions described in Table II employ an emulsion explosive comprising at least calcium nitrate and sodium nitrate. Emulsion explosives with other components as mentioned before are also feasible.

The range of raw materials for explosive compositions comprising heavy ANFO and plant derivatives (ie inert bulking and sensitizing additives) and having properties close to those of ANFO is given in Table II below.

Table II raw material Range ±1% weight ammonium nitrate 75 calcium nitrate 12 ^* sodium nitrate 12 ^* fuel phase 6.6 water 6.6 inert bulking agent 15 ^**

^* Maximum % of mixture of calcium nitrate and sodium nitrate is 12%

^** % relative to final blend of heavy ANFO and grain hulls

The range of raw materials for explosive compositions comprising heavy ANFO and plant derivatives (ie inert bulking and sensitizing additives) and having properties closer to those of ANFO is given in Table III below.

Table III More preferred constituents raw material Range ±1% weight ammonium nitrate 75.23 calcium nitrate 11.61 ^* sodium nitrate 11.61 ^* fuel phase 6.49 water 6.58 inert bulking agent 13.5 ^**

^* Maximum % of mixture of calcium nitrate and sodium nitrate is 11.61%

^** % relative to final blend of heavy ANFO and grain hulls

Now that the explosive composition has been described, the method of making the same will now be described. Typically, explosive compositions of heavy ANFO and plant derivatives (ie, inert bulking and sensitizing additives) are formed in a mixer. It is preferred that the explosive composition be prepared such that little mechanical stress is imposed on the components of the composition during preparation, while a high degree of uniformity is achieved, as this reduces variability in the performance characteristics of the explosive composition. It has been found that the mixer capable of preparing explosive compositions with a high degree of uniformity while exerting little mechanical stress on the composition components is an end-of-fill level mixer. Examples of such mixers are found in US 4506990, which is incorporated herein by reference. A mixer operating on a similar principle to the mixer mentioned in the '990 patent, and any mixer capable of achieving a high degree of homogeneity in a composition and exerting little stress on the components of the composition during preparation, is feasible. It will be appreciated that the explosive composition may be prepared and used as an explosive without a high degree of homogeneity or with little mechanical stress during preparation. However, if there is no high degree of uniformity and/or the composition is subjected to significant mechanical stress during preparation, the performance properties of the resulting composition will have a greater degree of variability.

The mixer operates on a mobile platform, enabling the explosive composition to be mixed at the blast site and then transported between blast holes at the blast site.

The mixer is also equipped with a directable chute, sleeve or auger to allow the explosive composition to be dispersed into the blast hole. It should be understood that the mixer could also be run on a fixed platform and then transferred to a mobile vehicle for delivery to the blast hole. However, the transfer operation subjects the explosive to unnecessary mechanical stress, which can adversely affect the performance of the explosive composition.

Regardless of the type of mixer used, explosive compositions are formed by mixing heavy ANFO and plant derivatives (inert bulking and sensitizing additives) comprising grain husks with many voids . More specifically, inert bulking and sensitizing additives are added to the heavy ANFO in a mixer and mixed with the heavy ANFO. Mixing was terminated when it appeared that the grain hulls were substantially evenly dispersed among the heavy ANFO particles.

Heavy ANFO in the mixer can be prepared at various locations and then loaded into the mixer. In many cases, however, it is preferred to prepare the heavy ANFO in the same mixer as the heavy ANFO and bulking and sensitizing additives are mixed. In this case, the preparation of the explosive composition begins by loading the emulsion explosive into the mixer. Emulsion explosives have a bulk density of about 1.26 to 1.50 gm/cc and an oxygen balance of about -7.5 to 1.0. The emulsion explosive also has about 10-25% water by weight. The mixer is generally not in operation during the loading of emulsion explosives.

After the emulsion explosive is loaded into the mixer, the ANFO and/or ammonium nitrate is loaded into the mixer. Usually the mixer is not working during loading of ANFO and/or ammonium nitrate. At least in the case of end level mixers, the ANFO and/or ammonium nitrate is loaded such that the ANFO and/or ammonium nitrate is on top of the previously loaded emulsion explosive. This reduces the mechanical stress on the ANFO and/or ammonium nitrate when starting the mixer, since the emulsion explosive lubricates the rotor of the mixer.

After the ANFO and/or ammonium nitrate is loaded into the mixer, the mixer is operated to mix the emulsion explosive with the ANFO and/or ammonium nitrate, thereby producing heavy ANFO. In the end level mixer, mixing takes about 2 minutes. Heavy ANFO has a bulk density of about 1.0-1.45 gm/cc. It is generally believed that heavy ANFOs with bulk densities in this range, especially at the upper end of the range, are too dense to detonate reliably in certain applications.

After the heavy ANFO is made, the inert bulking and sensitizing additives, which consist of the highly porous grain hulls, are added to the heavy ANFO in the mixer and mixed as above. The admixture of additives with heavy ANFO reduces the bulk density of the explosive composition. The resulting explosive composition has a bulk density of about 0.35 to 1.33 gm/cc, depending on the amount of additive used. When using an end-of-level mixer, mixing of the heavy ANFO typically takes 4 to 12 minutes to complete before the heavy ANFO is mixed with the inert bulking and sensitizing additives.

The explosive composition is applied in mining operations by loading it with appropriate detonating means into one or more blastholes. Typically, the detonating device is loaded into the blasthole prior to loading the explosive composition into the blasthole. The blast engineer determines the amount of explosive to load into each blasthole and uses an on-board weighing system that delivers the explosive composition to one or more blastholes to load the correct amount of explosive composition into each blasthole middle. As mentioned above, the explosive composition can be prepared at the site of the detonation. Also, the explosive composition can be prepared on site on a mobile vehicle, which is then used to deliver the explosive composition into the blasthole.

Claims (33)

1. An explosive composition comprising: heavy ANFO comprising an explosive emulsion and an ammonium nitrate-based explosive; and Inert bulking and sensitizing additives comprising grain hulls each characterized by a large number of voids, wherein said inert bulking and sensitizing additive is substantially free of components of said grain other than said grain hull. 2. An explosive composition according to claim 1, wherein the explosive emulsion comprises an oxidizer, water, an immiscible fuel and an emulsifier. 3. An explosive composition according to claim 2, wherein said oxidizing agent comprises ammonium nitrate. 4. An explosive composition according to claim 2, wherein said oxidizing agent comprises calcium nitrate. 5. The explosive composition according to claim 2, wherein said oxidizing agent comprises sodium nitrate. 6. The explosive composition according to claim 2, wherein said immiscible fuel comprises a carbonaceous fuel. 7. An explosive composition according to claim 6, wherein said carbonaceous fuel comprises fuel oil. 8. The explosive composition according to claim 1, wherein said ammonium nitrate-based explosive comprises ammonium nitrate. 9. The explosive composition according to claim 1, wherein said ammonium nitrate based explosive comprises ANFO. 10. The explosive composition according to claim 1, wherein said grain hulls are waxy. 11. The explosive composition according to claim 1, wherein said grain hulls are rice hulls. 12. An explosive composition comprising: heavy ANFO comprising an explosive emulsion and an ammonium nitrate-based explosive; and Inert bulking and sensitizing additives comprising grain hulls, each characterized by a high number of voids; wherein the grain hulls are not naturally attached to any other components of the grain. 13. An explosive composition according to claim 12, wherein the explosive composition is substantially free of any other components of said grain. 14. An explosive composition according to claim 12, wherein said grain hulls comprise rice hulls. 15. An explosive composition according to claim 14, wherein said explosive composition is substantially free of any components of rice grain other than rice hulls. 16. An explosive composition comprising: Heavy ANFO comprising an explosive emulsion and an oxidizing additive including ammonium nitrate; and Inert bulking and sensitizing additives comprising rice hulls, each characterized by a high number of voids; Wherein said inert bulking and sensitizing additive is substantially free of other components of rice except said rice hulls. 17. A method of preparing an explosive composition comprising: Provide mixing equipment; loading said mixing device with emulsion explosive for the first time; After said first loading step, charging said mixing device a second time with ammonium nitrate-based explosive; mixing said emulsion explosive and oxidizing additives using said mixing equipment for the first time to produce heavy ANFO; After said first use step, the mixing equipment is used a second time to mix heavy ANFO with inert bulking and sensitizing additives comprising grain hulls, each characterized by a high number of voids. 18. The method of claim 17, wherein the step of providing mixing equipment includes providing an end level mixer. 19. A method of preparing an explosive according to claim 17, wherein during said first loading step said mixing device is inactive. 20. A method of preparing an explosive according to claim 17, wherein during said second loading step said mixing device is inactive. 21. The method of preparing explosives according to claim 17, wherein said mixing device is inactive during said first loading and second loading steps. 22. The method for preparing an explosive according to claim 17, wherein said first loading step comprises loading an emulsion explosive having a bulk density of 1.26 to 1.50 gm/cc. 23. The method for preparing an explosive according to claim 17, wherein said first loading step comprises loading an emulsion explosive having an oxygen balance of -7.5 to 1.0. 24. The method of preparing an explosive according to claim 17, wherein said first loading step comprises loading an emulsion explosive containing about 10 to 21% by weight of water. 25. A method of preparing an explosive according to claim 17, wherein said second loading step comprises loading ammonium nitrate. 26. The method of preparing an explosive according to claim 17, wherein said second loading step comprises loading ANFO. 27. The method of making an explosive according to claim 17, wherein said grain hulls comprise rice hulls. 28. A method of preparing an explosive composition comprising: Provide terminal level mixer; Using the end level mixer, heavy ANFO was mixed with inert bulking and sensitizing additives including rice hulls. 29. The method of claim 28, further comprising mixing an emulsion explosive and an ammonium nitrate based explosive using said end level mixer to produce said heavy ANFO. 30. A method of using explosives in mining operations, comprising: providing an explosive composition comprising heavy ANFO and rice hulls; and The explosive composition is loaded into blastholes established in the ground. 31. The method of claim 30, wherein said providing step includes mixing said heavy ANFO and rice hulls. 32. The method according to claim 31, wherein said mixing step comprises mixing heavy ANFO and rice hulls on the same footprint as the blasthole is arranged. 33. The method of claim 31, wherein said mixing step comprises mixing heavy ANFO and rice hulls on a moving platform.